Alterations of amine neurotransmitter systems (norepinephrine (NE), serotonin (5HT) and dopamine (DA)) have been indirectly implicated in the pathophysiology of the major mental illnesses, depression and schizophrenia. We have applied new techniques to study cerebrospinal fluid (CSF), plasma and urine from drug-free patients with affective illness and schizophrenia using more sensitive and comprehensive characterization of the neurotransmitter systems. Careful control of sources of variance continues to produce new lines of evidence consistent with neurotransmitter dysregulation in mental illness: 1. Bipolar vs unipolar depressed patients are consistently found to have lower NE or its metabolite, MHPG, in CSF, plasma and urine, providing strong support for a hypothesis that these subgroups are biochemically distinct. 2. The NE response to physiologic stress is exaggerated in both bipolar and unipolar depression, indicating dysregulation of the system independent of the basal output of NE. 3. We now show high correlations between MHPG in urine, CSF and plasma--evidence against viewing any site as providing differential information. 4. Increases in plasma HVA, a major dopamine metabolite, are associated with poor response to treatment and/or the appearance of psychosis, providing direct biochemical support for a longstanding hypothesis. 5 Initial carefully controlled studies reveal a much clearer circadian rhythm in plasma HVA than MHPG. This is of particular interest since the plasma HVA rhythm appears to coincide with hormonal synthesis of hormones under dopaminergic control.